In his first-ever interview, the sole Australian survivor of the Waco siege has revealed to 60 Minutes what really took place during the 51-day stand-off, and why he believes crazed cult leader David Koresh will one day return to Earth as the son of God.

Scores of asylum-seeker families face being returned to Nauru after the High Court rejected a legal challenge to Australia's offshore immigration detention regime.

The full bench of the High Court handed down its ruling on Wednesday after considering the case of a pregnant Bangladeshi asylum seeker who was brought to Australia from Nauru for treatment of serious health complications.

Protesters have gathered to fight the decision. (AAP)

She faced the prospect of being returned to the Pacific island with her one-year-old child.

However, the ruling also has implications for 267 people - including 91 children - who were also brought to Australia for medical treatment.

The federal government, with Labor's support, had retrospectively changed laws to shore up the Commonwealth's ability to pay for the offshore facilities.